H. S. Williams — Crustacean from the Devonian. 47 



spines (C), which are nearly parallel with the axis of the body 

 and reach nearly to a point opposite the posterior margin of 

 the buckler. The cephalic shield along the median line is 

 about a third the length of the body ; (M K) the space between 

 the posterior margin of the cephalic shield and the anterior 

 margin of the buckler containing the region of the mouth (M) 

 and the gnathopods (K), and (F D H) the thoracico-abdominal 

 buckler, marked over the surface by longitudinal ridges and 

 by marginal spines, and terminating in a long stout telson (B). 

 Traces of the gnathopods are seen, as also traces of the folia- 

 ceous appendages of the posterior pair(L), but in too imperfect 

 condition for exact delineation, just anterior to the position 

 of the mouth is seen a shield-like elevation (B), upon the edge 

 of the cephalic shield, which has the appearance of an hypos- 

 toma. The condition of the specimen is not such as to give 

 absolute certainty to this interpretation, though the symmetry 

 of its form is strongly in favor of it. It is possible that it is 

 merely outlines upon the surface produced by crushing during 

 fossilization. There are faint indications of joints on each of 

 the anterior set of gnathopods (K K). 



Along the center of the thoracic region (H), there is a flat- 

 tened depression, traversing longitudinally from the anterior 

 edge of the plate F, backward to the middle of the telson E. 



The terminal portion of the telson is evenly rounded. Each 

 side of the median line of the buckler there are visible four 

 clearly defined marginal spines (g g) ; there were probably more 

 of them — six I have supposed, as in fig. 3, but concealed in 

 the specimen by the filling between the buckler and genal 

 spines. 



There are also four rounded, longitudinal ridges on the 

 buckler each side of the flattened depression H : these (ii) 

 begin abruptly near the anterior margin of the buckler and 

 run almost directly backward, tapering to a slender point near 

 the margin of the buckler. 



At the anterior margin of the buckler there is a narrow 

 plate, divided into a median and two lateral parts (F), which 

 appears to be separated from the buckler itself by a distinct 

 furrow. Laterally this plate appears to curve inward and lies 

 below (within) the surface of the buckler, and the median por- 

 tion extends forward to a blunt point. I have interpreted this 

 as probably representing the consolidated lamellar appendages 

 of the "first and second" thoracic segments of Eurypterus, as 

 defined by Hall in Paleontology of New York, vol. iii, p. 398. 



The telson E, is nearly two-thirds the length of the body, is 

 flattened at the base, but nearly cylindrical and tapering to a 

 blunt point at the extremity. There is no indication of its 

 articulation, but there is no reason, from the condition of the 

 specimen, to presume that it was not articulated. 



